1. Field of the Invention
The present invention relates to structures having a roof which may be opened and closed. In particular, the invention relates to a roof which is made of rigid panels which nest together when opened and which partially overlap when closed.
2. Revue of the Art
In an effort to provide a more enjoyable environment within a building, structures have been built having a roof which may be opened and closed. Stadium structures are especially well suited to such roof systems since spectators and players generally prefer to be exposed to sunlight and breezes but when the weather turns inclement a sheltered environment is preferred. Stadium structures having a fixed partial roof represent an increasingly unacceptable compromise between these two preferences and therefore stadiums having moving retractable roof panels have been developed. Although any building or enclosed space can be constructed having a retractable roof, over an atrium or promenade for example, economic considerations have dictated that large retractable roof structures be restricted to stadiums. Such a roof eliminates the need to cancel or reschedule games or concerts due to inclement weather and in addition the attendance at such events increases since spectators are more willing to attend if retractable shelter is provided.
An example of a stadium having a retractable rigid panel roof is the SkyDome.TM. stadium in Toronto, Canada as described in U.S. Pat. Nos. 4,676,033 issued June 30, 1987 and 4,716,691 issued Jan. 5, 1988. The SkyDome stadium has one fixed roof panel approximating a quarter spherical shell, and three moving roof panels which move upon rails positioned in a horizontal plane supported upon the upper portion of the stadium building. In the closed position, the roof panels form an egg-shaped roof having the fixed quarter spherical panel at one end and a moving quarter spherical panel at an opposite end with two arching panels in the middle portion of the roof. In the open position the roof panels are moved to nest within each other over the fixed roof panel. Since the roof panels of the SkyDome stadium move in a horizontal plane relatively little power is required to move the panels upon their bogie wheels, but the distance the panels must move and their movement sequence make the opening and closing process relatively slow.
Several disadvantages are apparent in the SkyDome type design. The roof structure is supported upon the upper portion of the stadium building requiring that a substantial portion of the stadium be constructed before commencing roof erection thereby lengthening construction schedules, and that the stadium building itself carries the roof loads. The roof panels must be erected at their final elevation requiring ironworkers and cranes to work at substantial elevations which inevitably reduce the speed of erection. When such a stadium is constructed in an area prone to earthquakes the stadium building and roof must both be interconnected and designed in such a way as to withstand significant accelerations and vibrations. Each panel should be designed to withstand earthquake loads in a partially or fully open position, as well as in a closed position.
A further disadvantage of such a roof structure is the presence of the fixed panel. Even when positioned to cast the least shadow possible, the retracted panels nested above the fixed panel still reduce the effect of the open roof in significant areas of the stadium. In order to fully retract the two middle panels, a track is built beyond the walls of the stadium and the middle panels extend beyond the stadium in their fully open position adding to the amount of land required to accommodate the structure.